I've been using Muraena for a couple months now and I like it. The interface is nice. The searches are easy and the export process is simple. A couple of the features that I really like are the option to remove previously downloaded contacts and the filter that eliminates contacts that don't have a business email address.

Here is my word of caution. Make sure that you use a third-party email verifier. My experience is that over 5% are nondeliverable and an additional 25% are classified as risky. The other 70% are valid but only 25% of those are rated as "Safe to Send" by the Email Verifier I Use. So, use caution before sending out mass emails.